New Evidence Strengthens The Case For Dark Matter Particles

The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe. These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case. This image was composed from data from the Digitized Sky Survey 2.

An international group of astronomers have conducted a series of observations on the dark matter distribution in dwarf galaxies, the diminutive companions of much larger galaxies like ours. What they discovered will likely start many discussions in astronomy. They found that the distribution of dark matter is dependent on the evolution of the stars in these galaxies.

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This is a big deal. Dark matter is, as the name states, dark. It is only affected by gravity, and it influences the shape and structure of galaxies. But in this case, the “light” components affect it back. Galaxies with a lot of star formationhave less dark matter in their cores. Galaxies that instead stopped forming stars a long time ago have denser dark matter cores. The findings are reported in the Monthly Notices of the Royal Astronomical Society.

The team looked at 16 dwarf galaxies with different stellar evolution histories. The observations suggest that the most star-forming galaxies, and thus those that have experienced the highest number of supernovae, have less dark matter in their cores. This is possibly because during star formation, stars push gas and dust to the outskirts of galaxies. When the gravity at the center of these small galaxies gets smaller, dark matter gains energy and spreads out, following regular matter.

“We found a truly remarkable relationship between the amount of dark matter at the centres of these tiny dwarfs, and the amount of star formation they have experienced over their lives. The dark matter at the centres of the star-forming dwarfs appears to have been ‘heated up’ and pushed out,” lead author Professor Justin Read, head of the Department of Physics at the University of Surrey, said in a statement.

The effect is being referred to as “dark matter heating”, but it’s not really about dark matter getting warmer, it’s about gaining energy. The findings could be key to reducing the number of dark matter models. Could such a variety of dark matter densities form in dwarf galaxies in any specific model?

“This study may be the ‘smoking gun’ evidence that takes us a step closer to understanding what dark matter is. Our finding that it can be heated up and moved around helps to motivate searches for a dark matter particle,” Professor Matthew Walker, co-author from Carnegie Mellon University, added.

This is not the final word on the matter, rather a stepping stone. The team would like to significantly expand this work to include more galaxies, including smaller and more distant ones. The ambitious goal is to create more constraints for dark matter models.